Broad Challenge Area-Translational Science (15) Specific Challenge Topic- 15-OD(ORDR)-101*: Pilot projects for prevention, early detection and treatment of rare diseases, Syphilis is a chronic, multisystemic disease caused by the spirochete, Treponema pallidum subspecies pallidum (T. pallidum). The spirochete is acquired by sexual contact and is prevalent worldwide. Congenital syphilis and neurosyphillis manifestation of the disease have become rare in the Western countries but they remain a problem in underdeveloped countries of Africa, Central Asia and Eastern Europe. Congenital syphilis is devastating and can result in stillbirths, abortions, low birth weights or premature births. Neurosyphillis is also re-emerging around the world. T. pallidum sequence revealed itself to be one of the smallest genomes (1.1Mb) among bacteria with a few potential surface proteins that can determine the spirochete's ability to colonize various tissues during infection. Spirochetes are extracellular pathogens and their adherence to mammalian cells appears to play a critical role in tissue colonization. However, several challenges have resulted in the poor understanding of T. pallidum pathogenesis. (i) T. pallidum cannot be grown in vitro. This limits the ability to investigate this organism thoroughly. (ii) Genetic techniques are not feasible for this spirochete. (iii) T. pallidum exhibits extreme host specificity with humans as its only natural host. Therefore, there is a desperate need to develop novel strategies to investigate the molecular basis of T. pallidum pathogenesis especially relevant to congenital syphilis and neurosyphillis using a small animal model system. T. pallidum is closely related to Borrelia burgdorferi, which causes Lyme disease. Both of these spirochetes are structurally and physiologically similar organisms and share several homologous proteins. T. pallidum and B. burgdorferi exhibit different phases of disease in their hosts, including disseminated infection of various tissues followed by latent and chronic disease. Development of genetic tools for B. burgdorferi in the past decade has led to a significant progress in the understanding of Lyme disease pathogenesis. In this proposal, we will employ a highly innovative and unconventional approach of using bioluminescent B. burgdorferi as a surrogate system to study the role of selected T. pallidum molecules in cell-specific interactions and pathogenesis. Our hypothesis is that expression of one or more T. pallidum proteins in bioluminescent B. burgdorferi will promote invasion and colonization of specific sites. Invasion of the placenta, which may lead to congenital transmission and of the central nervous system will be detectable in mice by an in vivo imaging system (IVIS 200). The following studies will test this hypothesis. Specific Aim 1: To examine the expression and localization of T. pallidum proteins in B. burgdorferi and assess their roles in adherence to specific mammalian cell lines in vitro. Specific Aim 2: To determine if B. burgdorferi acquires the ability to colonize brain and placenta of mice efficiently after expression of T. pallidum protein(s) and also promotes congenital transmission of Lyme spirochetes from placenta to the litter. Significance Development of a new bioluminescent B. burgdorferi surrogate model system in this proposal will help visualize disseminated colonization of the mouse placenta and neuronal tissues facilitated by the expression of T. pallidum proteins. This gain of function approach will help fill the gap in the understanding of this historic, uncultivable spirochete. Furthermore, there are no promising vaccine candidates identified against syphilis to date. We expect that our experience in B. burgdorferi and expertise of our collaborators, Drs. Sheila Lukehart and Arturo Centurion, in T. pallidum pathogenesis will help us achieve our objective to identify critical virulence factors of T. pallidum and determine their potential as diagnostic markers and novel vaccine candidates. PUBLIC HEALTH RELEVANCE: Syphilis is a chronic multisystemic disease and congenital syphilis and neurosyphillis manifestation of the disease are rare in the Western countries. Congenital syphilis is devastating and can result in stillbirths, abortions, low birth weights or premature births and neurosyphillis is also re-emerging around the world. Using bioluminescent bacteria as surrogate system to express uncultivable syphilis-causing spirochete proteins in this proposal will facilitate examination of colonization of mouse placenta and neuronal tissues and will also help in identification of new diagnostic markers and vaccine candidates.